Optically-stimulated luminescence profiling and dating of historic agricultural terraces in Catalonia (Spain)

Dating agricultural terraces is a notoriously difficult problem for archaeologists. The frequent occurrence of residual material in terrace soils and the potential for post-depositional disturbance mean that conventional artefactual and lab-based dating methods often provide unreliable dates. In this paper we present a new technique using luminescence field profiling coupled with OSL dating to produce complete (relative) sequences of dates for sedimentary stratigraphies associated with agricultural terraces and earthworks. The method is demonstrated through a series of case-studies in western Catalonia, Spain, in which we reconstruct the formation sequence of earthwork features from the Middle Ages through to the present day. OSL profiling at the time of archaeological survey and excavation permitted spatially and temporally resolved sediment ‘chronologies’ to be generated, and provides the means to interpret the environmental and cultural archives contained in each. The case-studies presented here show that luminescence approaches are a valuable tool to reconstruct landscape histories

The coevolution of toxin and antitoxin genes drives the dynamics of bacterial addiction complexes and intragenomic conflict

Bacterial genomes commonly contain ‘addiction’ gene complexes that code for both a toxin and a corresponding antitoxin. As long as both genes are expressed, cells carrying the complex can remain healthy. However, loss of the complex (including segregational loss in daughter cells) can entail death of the cell. We develop a theoretical model to explore a number of evolutionary puzzles posed by toxin–antitoxin (TA) population biology. We first extend earlier results demonstrating that TA complexes can spread on plasmids, as an adaptation to plasmid competition in spatially structured environments, and highlight the role of kin selection. We then considered the emergence of TA complexes on plasmids from previously unlinked toxin and antitoxin genes. We find that one of these traits must offer at least initially a direct advantage in some but not all environments encountered by the evolving plasmid population. Finally, our study predicts non-transitive ‘rock-paper-scissors’ dynamics to be a feature of intragenomic conflict mediated by TA complexes. Intragenomic conflict could be sufficient to select deleterious genes on chromosomes and helps to explain the previously perplexing observation that many TA genes are found on bacterial chromosomes

Supply constraints on rebound effects of increased energy efficiency : negative multiplier and disinvestment effects

Policies that aim to use increased energy efficiency to reduce energy use may not achieve the desired results due to the likelihood of rebound effects. Research from our current ESRC-funded project on this topic was presented in an article in the last issue of Fraser Economic Commentary titled, ‘Energy Efficiency and the rebound effect’ (Turner, 2009a). As explained there, the rebound effect occurs when an energy efficiency improvement causes a decrease in the effective or implicit price of energy as an input to production (or consumption) – i.e. the cost of energy required per unit of activity falls as efficiency improves.1 Moreover, if there is local production/distribution of energy (or energy services) the reduction in demand for energy as efficiency improves will put downward pressure on the actual (local) energy price

Changes and continuities in a Mediterranean landscape : a new interdisciplinary approach to understanding historic character in western Catalonia

This work was supported by Ministerio de Economía y Competitividad, Spain [grant number MINECO HAR2012-35022].To understand why historic landscapes changed in the past researchers need to identify when and where changes took place, but in rural landscapes, the origins and development of many historic elements including field systems, roads, terraces and other earthworks remain poorly understood. This paper outlines a practical interdisciplinary method using GIS-based historic landscape characterisation (HLC) to integrate data from different sources and model how historic character varies in space. It pilots an innovative approach using luminescence profiling and dating that can underpin the HLC with significantly improved knowledge of historic processes of change. We focus on four case studies of terraced agricultural landscapes in western Catalonia and demonstrate for the first time that existing terrace systems often have medieval or early modern origins.Publisher PDFPeer reviewe

Chatter, process damping, and chip segmentation in turning: A signal processing approach

An increasing number of aerospace components are manufactured from titanium and nickel alloys that are difficult to machine due to their thermal and mechanical properties. This limits the metal removal rates that can be achieved from the production process. However, under these machining conditions the phenomenon of process damping can be exploited to help avoid self-excited vibrations known as regenerative chatter. This means that greater widths of cut can be taken so as to increase the metal removal rate, and hence offset the cutting speed restrictions that are imposed by the thermo-mechanical properties of the material. However, there is little or no consensus as to the underlying mechanisms that cause process damping. The present study investigates two process damping mechanisms that have previously been proposed in the machining literature: the tool flank/workpiece interference effect, and the short regenerative effect. A signal processing procedure is employed to identify flank/workpiece interference from experimental data. Meanwhile, the short regenerative model is solved using a new frequency domain approach that yields additional insight into its stabilising effect. However, analysis and signal processing of the experimentally obtained data reveals that neither of these models can fully explain the increases in stability that are observed in practice. Meanwhile, chip segmentation effects were observed in a number of measurements, and it is suggested that segmentation could play an important role in the process-damped chatter stability of these materials

Clustering in 18O - absolute determination of branching ratios via high-resolution particle spectroscopy

The determination of absolute branching ratios for high-energy states in light nuclei is an important and useful tool for probing the underlying nuclear structure of individual resonances: for example, in establishing the tendency of an excited state towards α -cluster structure. Difficulty arises in measuring these branching ratios due to similarities in available decay channels, such as ( 18 O, n ) and ( 18 O, 2 n ), as well as differences in geometric efficiencies due to population of bound excited levels in daughter nuclei. Methods are presented using Monte Carlo techniques to overcome these issues

The role of tool geometry in process damped milling

The complex interaction between machining structural systems and the cutting process results in machining instability, so called chatter. In some milling scenarios, process damping is a useful phenomenon that can be exploited to mitigate chatter and hence improve productivity. In the present study, experiments are performed to evaluate the performance of process damped milling considering different tool geometries (edge radius, rake and relief angles and variable helix/pitch). The results clearly indicate that variable helix/pitch angles most significantly increase process damping performance. Additionally, increased cutting edge radius moderately improves process damping performance, while rake and relief angles have a smaller and closely coupled effect